All I Need
by Amelia Reds
Summary: There seems to be a rivalry between Head Boy Jim Moriarty and Sherlock Holmes, but John had no idea why. It only took a night stroll and a touch to find out that not everything is as it seems. Potter!verse
1. Chapter 1

**Lalalala, so this is a one shot Johniarty. *EDIT* Was a one shot. But I seem to be uncapable of writing one shots now. This will be multi chap. *EDIT* Don't like. Don't read, ehehe. HP universe. Apologies for mistakes. Doing this without the power of research.**

**Disclaimer: None of the characters belong to me.**

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><p>Time management had never been his forte as shown by today.<p>

John had been meaning to study, but then Sherlock had caught onto a murderer at Diagon Alley and of course the Gryffindor had to follow him as they chased him down. After that, John went to Muggle London to buy candy that wouldn't explode or jinx him due from Sherlock's experiments. When he returned, he had found out that Sherlock had foolishly tried to start a fight with Head boy James Moriarty again and ended up with a broken nose.

After giving Sherlock a scolding and healing his broken nose, they had headed down to the field to watch the Slytherins train, but of course, Moriarty had been there. Sherlock, despite being a Ravenclaw, stupidly walked up to the Head Boy and landed a punch on his face before John had the chance to stop him.

John had rushed to the Slytherin despite Sherlock telling him not to, already with his wand out, healing spell on his lips. Moriarty was sitting up, one hand reaching for his wand as the other wiped away the blood pouring from his nose.

"Moriarty, can I help?"

Before waiting for a reply, John touched the boy's cheek. The second John's hand made contact, Moriarty's eyes snapped open to meet John's eyes, hands twitching. The Gryffindor remained oblivious, casting a spell to fix his nose.

After that, Professor Malfoy escorted Sherlock and Moriarty to the Headmaster Granger's office, leaving John to finally sit down and study. The only problem was that Mary Morstan had seemed determined to convince John that she was the one he should invite to the Halloween Ball.

It took an hour and a promise of a date to reassure her that maybe he would go to Halloween Ball with her. Just as he had all his supplies ready to study, Madam Hudson came and told him the library was closing.

"But, Madam Hudson, I need to study for tomorrow's Potions exam." John pleaded. "Can't you give me like thirty more minutes please."

Madam Hudson sighed before reaching into her pocket. She took out a key and with a wave of her wand duplicated it.

"I trust you, dear, and I understand how it can get noisy at the common rooms. Go to bed before 11, and close the library doors once you're done." She ordered and John nodded eagerly. She smiled and ruffled his hair.

"Good night, John. I'm going to lock the doors behind me so that no one else comes back in."

"Thank you, Madam Hudson."

The librarian nodded and waved goodbye.

With that, the Gryffindor opened his textbooks and began to speed read the books. Sherlock may be able to see something once and classify it for later, but John was normal. He had to study and reread and go over things, because unlike Sherlock he did not have a photographic memory.

Somewhere between how to make Polyjuice Potion and its side effects, John began to think about what had happened earlier. Sherlock wasn't the type to just hit someone for no reason, and yet, when it came to the Head boy, he seemed to lost all inhibitions.

It had started earlier this year after the fall. Sherlock and Moriarty were constantly arguing in class, or rather Sherlock was always arguing with Moriarty while the other smirked and taunted him. Despite all this, there seemed to be an undercurrent tension and issue John didn't know about. Moriarty was one of the best students at Hogwarts, with an intelligence rivalling Sherlock's, but he did seem to be a little off. There was something wrong about him. Moriarty had plenty of friends though they seemed to be more like followers.

John shook his head and tried focusing again, but he was bored by the text. Maybe a walk around the lake would help then he could come back in to finish the chapter at least.

He left his things on the table and pocketed the key to the library after locking it close. Swiftly, he ran down the stairs and to the lake. It was beautiful at night time, the moon reflecting of the water's surface. John walked around the edge, closing his eyes with a smile.

Finally, a bit of relaxing time.

The air around him suddenly dropped and John frowned, opening his eyes. Why had it suddenly gotten cold? His answer came to him as he saw a Dementor coming towards him. How had a Dementor gotten on grounds? The Gryffindor scrambled back, reaching for his wand, but it was too late.

Pain and sadness ripped through John as the Dementor began sucking out the happy memories. John felt tears sliding down his cheeks, and his hands clenched but he was immobile. The ground beneath him shifted quickly and he felt himself sliding into the freezing water. He felt as if he were turning into ice, with the Dementor freezing his inside and the cold water freezing his outside. It was when he was chest high that he heard footsteps running his way.

"Watson!" a voice shouted. "Expecto Patronus!"

The Dementor screeched, letting go of the Gryffindor, and as John crumbled into the water, he saw a fox chasing it down. A pair of hands frantically grabbed John and pulled him out of the water, laying him down on the ground. Fingers caressed John's face and his name was being repeated. Why did his voice sound so familiar?

"John, come on. Open your eyes. Say something, Watson. "

He opened his eyes as he finally identified the voice. Moriarty.

"Moriarty." He coughed, trying to sit up. The Slytherin helped him up, quickly chucking off his robes.

"Fuck, you're alright." Moriarty wrapped his robes around John. The blond froze as the Head Boy ran his hands through John's sopping hair. "Thought I had lost you for a second."

"Moriarty?" John coughed as Moriarty moved back, cupping John's face.

"Why were you even out here, you idiot? Alone, no less?!" His voice went dark, and John flinched at the malicious tone.

"I was studying and wanted to go for a walk." John blushed at the little distance between their faces, feeling overwhelmed.

"You were almost killed! What if I hadn't gotten there in time, Watson? For Merlin's sake, you are such an imbecile" He hissed, sounding furious. John winced. He may not have been as smart as Sherlock but to hear it from someone else hurt.

"I'm sorry." John found himself shuddering at the warmth Moriarty was giving off through his hands. Even with the robes he had given him, John was shivering.

The Head boy noticed this and tugged him towards the castle.

"Let's get you warmed up."

John sleepily let him guide him back to the castle. He was somewhere on the thin line between sharp clarity and heavy drowsiness. It took him a second to realize he was not being led to the Gryffindor dormitories but down to the dungeons.

"Where are you taking me, Moriarty?"

"Jim."

John frowned in confusion.

"Moriarty makes me sound like a creep. Call me Jim." He smirked, and John couldn't help the blush on his cheeks.

"Where are you taking me... Jim?"

"Head Boy rooms."

There was no explanation and John just tiredly followed him, stumbling on the steps which caused him to bump into Jim.

"Sorry." John muttered.

"We're almost there." Jim smirked as they approached the Head Boy's room. "You can sleep on my bed and I'll sleep on the couch, yeah? I can bring you some chocolate from the kitchen."

John chuckled and shook his head, head pounding.

"Thank you." John smiled as Jim whispered the password to the door which opened a second later. As they entered, John's vision suddenly dizzied and he was suddenly being held in Moriarty's arms.

"Damn," the Head Boy cursed as he sprinted to his bedroom John shaking violently. "John, I need you to stay awake for me. Talk to me. You close your eyes and you will die."

John could faintly feel Jim placing him on the bed and his clothes being ripped from him. Everything was freezing and a sudden painful pinch brought him back from the darkness he had been creeping into.

"John, talk."

John groaned.

"Cold. Tired. Let me sleep, Jim... I think I left my things in the library. Madam Hudson is going to kill me. Dementor was so cold. Hurt. Then you were there." John murmured as he opened his eyes to find a dishevelled Jim bringing in some more blankets from his closet. He also realized that somewhere between the door and now, he had been changed out of his soaked clothes and into some pyjamas that were too big for him.

"Sorry I got your clothes wet."

Jim blinked and let out a laugh.

"I don't think that's what's most important right now." He put the extra blankets over John whose vision was beginning to blur.

"Thanks for saving me."

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><p><strong>And with those last slurred words, John slipped into unconsciousness.<strong>

**So there is a plot to this, but it doesn't come until the next chapter.**

**Thanks for reading this and review! Review= faster updates (if wifi permits)**

**-Mel Reds**


	2. Chapter 2

**So, I've gotten many enthusiastic reviews, which have really made my day, and with school, updates are going to be even slower since I won't be able to go to a Starbucks or McDonalds for free wifi whenever I want.**

**I'll try to continue to write but I have so many advanced courses this year, so sorry, but I will use all my spare time writing. **

**Thanks and keep reviewing! /(^_^)/**

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><p>There was something warm on his forehead... And damp. It took John a moment to fully come awake, but the first thing he felt was a hand sifting through his hair. John moved to get up and the hand snapped away from him and the Gryffindor found himself looking up at the Head boy with bleary eyes. He stared blankly at him, trying to figure out why he was here.<p>

"Moriarty?"

Jim sighed.

"Really, Johnny-boy? Is that all you can say? All last night you were saying was Moriarty. Does your vocabulary consist of my last name?" His dark eyes held an amused gleam in them and he held out a chocolate bar.

"What happened last night?" John sneezed. He looked around the room, taking in the simple design it had. The main colours were green, black, and silver, and the only other thing besides the bed was shelves full of books, both Wizard and Muggle, John noticed surprised.

"You were attacked by a Dementor and almost drowned in the lake. I brought you to the Head Boy Quarters. You were barely even able to make it here." Jim smiled as John took a bite of the chocolate. The flavour exploded in his mouth and he moaned.

"Thank you, Moriarty"

"I do have a first name." The Slytherin commented drily as he stood up, stretching. His clothes were rumpled and there were dark circles under his eyes. Had he stayed up all night to look after him?

John blushed.

"Thank you, Jim."

"You're most welcome." Jim smirked as he sat down again and leaned his elbow on the arm of the chair.

For a few seconds neither of them said anything, they both just stared at each other, eyes locked solely on the others. John's hands were itching to touch Jim again, but he kept them tightly clenched next to him. Jim, on the other hand, seemed to have no qualms about touching him as he put his fingertips on John's forehead, lightly dragging them across his skin as if he were caressing him. The Gryffindor's eyes fell shut without his permission.

"You don't seem to have a fever." Jim smirked as he drew away and John almost protested.

"Yeah," John cleared his throat, turning beat red as he looked down at his hands. Why did he long for Jim's touch?

Suddenly, there were footsteps coming their way and Jim bolted to his feet and turned around, placing himself between John and the door which opened a second later.

"Am I right to presume I am not interrupting a slumber party?" The voice sneered.

Professor Holmes was by far the teacher that scared John the most. It wasn't his intelligence or cold demeanour that terrified John but the look of absolute hatred he gave John. He taught Defense Against Dark Arts and Wizarding Government.

It had all started when Sherlock and he had first become friends. Up until that point, Professor Holmes had only looked at John like any other student. It wasn't until John was cornered at the back of the library that this side of Professor Holmes showed. He had offered John money to stay away from Sherlock but the Gryffindor vehemently refused, which then led the professor to begin telling him all about John's past. John was unimpressed, considering Sherlock had already done this deduction trick. Their meeting had ended with Professor Holmes saying there would be consequences should John put Sherlock in danger.

"Professor Holmes, this is not what it looks like." Jim hooked his thumbs into his pockets. "I found Johnny-boy half drowning and being attacked by a Dementor. The Gryffindor Common Room was too far so I brought him here."

Professor Holmes pursed his lips together and placed the tip of his umbrella on the ground, a look of disdain on his face.

"Mr. Watson, get up. I'm taking you to the Infirmary, where you should've been taken from the beginning." He threw a pointed look at Jim.

John threw off the covers, blushing as he realized he was still wearing Jim's clothes. He stood up and Jim threw an arm around his shoulders.

"Doesn't he just look delectable in my clothes, Professor?" Jim purred, nosing John's neck. The Gryffindor looked about ready to die of mortification.

"Where are his clothes, James?" Professor Holmes asked, looking around the room.

"I sent them down to the elves to get cleaned. They were covered in mud and slime."

"I'm sure." He sneered, taking John by the arm and leading him out of Jim's room.

"Bye, Johnny Boy!" Jim laughed. "See you."

John was hauled out of the room and towards the stairs leading back to the main level, his feet stumbling on the way and vision dizzying. Professor Holmes was walking faster than usual as if he didn't want to be caught with John.

By the time they reached the Infirmary, John was out of breath and felt like he was going to throw up. The professor stopped at the door before turning around and facing John with the coldest look he had ever seen.

"Let me make this clear to you, . It's bad enough that my brother won't take my warning and steer clear of you. You're trouble. James Moriarty is one of the best Slytherin students this school has. He has enough responsibilities as it is without having to take care of a Muggle Gryffindor who can't keep out of trouble. Stay away from Sherlock and James."

With that, Professor Holmes turned on his heel and opened the doors to the Infirmary, leaving a shocked John in his wake.

John bit his lip as he walked in behind the professor who was already talking to the nurse. The woman rushed over to him and herded him to a bed, laying him down, a hand on his forehead. John found himself comparing it to the Jim's fleeting fingertips.

"You seem to be alright now. I think it would be safe for you to go, Professor-" The nurse turned.

John wasn't surprised to find him already gone. Why did Professor Holmes hate him? He hadn't done anything.

"The poor dear," the nurse chuckled as she handed John a bottle. "He's always busy, running around. Being the Head of Slytherin and professor of two subjects isn't easy let me tell you." She smiled. John immediately felt better as he gulped down the potion.

"He doesn't seem to like me much." John muttered as she cast a diagnostic spell over him.

"You're a Muggleborn, right?"

John nodded.

"One year after he graduated from Hogwarts, his parents were killed by a Muggle thief. Ever since then, he's had this prejudice against Muggles." The nurse softly said. "It's not that he really hates you, but he isn't comfortable with your heritage. He doesn't discriminate, mind you." She helped him up.

"That's why he is so protective of Sherlock." John realized.

Her eyes softened.

"Father at the age 18 of an 11 year old boy. I would be protective too. But that was years ago. You seem to be fine. Just take this potion tonight to ensure your body temperature doesn't suddenly plummet, and you should be good to go to class." She patted his head and John took the bottle gratefully.

"Thank you."

"No problem, dear. Now go to class, your first period is about to start. Here let me write you a pass." The nurse scribbled a pass on a paper.

"Professor Holmes could've gone to become a great leader." She said softly as she handed him his pass.

"John!"

The Gryffindor turned to find himself suddenly staring at the Ravenclaw crest, before being dragged out of the Infirmary.

"What did he do?" Sherlock demanded, turning around to face him once they were out in the hallway.

"I'm doing great, thanks for asking." John rolled his eyes.

"I know you're alright. Did Moriarty do anything? Did you accept Fatcroft's money this time?"

"I was attacked by a Dementor and almost drowned in the lake, but Jim-"

"Jim?!" Sherlock almost squeaked. "He's ensnared you too. Moriarty is a criminal mastermind, John. He has a whole army ready behind him to start a war."

"He saved me, Sherlock."

"Of course he did, John. Don't you see? He's trying to infiltrate the enemy side by gaining your trust."

The Gryffindor sighed.

"And no, your brother didn't offer me money. He warned me to stay away from you and Jim."

This shut Sherlock up about the oncoming war.

"He asked you to stay away from Moriarty?"

John nodded. The Ravenclaw frowned but shook his head.

"Come along, John. You have to change so we can go to DADA." Sherlock tugged him along towards the Gryffindor dorms,

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><p><strong>Sooooo, yep. Tell me what you think of this so far. Or what you hope will happen! ;)<strong>

**Review and Follow/Subscribe! Thanks!**

**-Amelia Reds**


	3. Chapter 3

**So many ideas, so little time and school. I'm sorry that it's been ages. I'm going to try and write a little more but please be lenient on me. Anywho, here is your next chapter.**

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><p>Sebastian was used to Jim having his little "experiments" and odd fascinations with fellow students which typically ended their death but this was probably the strangest he had ever seen him. Even when Jim had been obsessing over Sherlock, it was nothing like how he was acting right now.<p>

It had started this morning when the Head Boy had sauntered down the stairs with a grin on his lips. Sebastian was ready for him to start about his next victim, but Jim was oddly silent. They had walked down to eat breakfast and had run into Sherlock and Watson.

This was the first clue that something had happened between yesterday and now. Watson had been wearing _Jim's clothes. _Jim walked by them without a second glance and even Sherlock had seemed confused.

Now, Jim and Sebastian were in their usual seats at the very back, and Sebastian wasn't the brightest but he was sure there was something between that Watson fellow and Jim. The second Sherlock's Mudblood had walked into the room Jim's eyes had lit up, and Sebastian wasn't going to lie, it was then that he knew something was wrong.

John was a Mudblood. He was everything that Jim abhorred, and so the only reasonable explanation as to why he would be acting like sappy fool in love would be because the maggot had managed to miraculously slip Jim an Amorentia potion or some other powerful love potion.

It was that second Watson turned around and met Jim's gaze who winked at him with a saucy grin. The Gryffindor turned back around, blushing red. Sebastian was brought back to the class when Professor Holmes put down the chalk.

"Class, you will be practising with each other today, seeing as we've gone over this spell for the last two weeks verbally. You will only disarm each other. If I see you doing anything else, I will not hesitate in sending you to the office." Professor Holmes sent a sweeping glance around the room before turning around and sitting down at his desk. "You will come up and tell me who your partner is and it will have to be someone you have not worked with yet."

Sebastian practically flew out of his desk, earning him a questioning look from Jim but Sebastian ignored it. He would free Jim from whatever spell he was put under.

"And who is your partner, Mr. Moran?" the professor asked, quill appearing in his hand, not even looking up.

"John Watson."

Sebastian turned around, schooling his features to a more neutral expression as he walked towards Watson who was scribbling something on his parchment.

"Hey, Watson, you're my partner."

The Mudblood looked up with a confused look on his face but stood up nonetheless.

Sherlock glared at Sebastian who ignored it and herded Watson to the practising area.

"You're Sebastian, right?" John asked, tilting his head as he turned to face the Slytherin.

"Yes."

"Well, um, I've already learned this spell, so you can go first." Watson smiled.

Sebastian seethed at the gall this idiot had. No matter, he would soon be disposed of. He was doing this for Jim.

They turned to face each other, wands ready, the Gryffindor with a confident look on his face.

Sebastian sent a silent Expelleriamus, and two seconds later, John's wand was in his hand and the Gryffindor was staring at him with shocked eyes.

"Wow, you're really good."

"I know." Sebastian smirked and threw aside John's wand, walking towards him. Watson frowned in confusion and the Slytherin revelled in the look of fear slowly coming onto his face as he came closer.

"What... What are you doing?"

The Gryffindor took a step back but Sebastian sent a Body-Binding Spell which locked him in place.

"Stay away from Jim." He growled. "Sectumsempra."

The second the words came out of his mouth, a blur pushed John out of the way and in front of him, the famous Ravenclaw Sherlock Holmes was being torn open, blood already spilling onto the floor. Screams tore out of his mouth and Sebastian stared in terror as ribbons of cuts spread over the Holmes's pale skin.

There were screams of terror from the other students and there were kids stepping towards Sherlock who was having a spasm.

"Sherlock!"

The Slytherin was pushed out of the way as Professor Holmes kneeled down next to him.

Sebastian felt a hand grab his shoulder and twist him back. With a hand on his neck and the other digging painfully into his shoulder, Sebastian was met with Jim's angry eyes. His hands were magically bound together and put behind his back.

Everybody thought that Sebastian was supposed to be like a bodyguard for Jim but the truth was that Jim could protect himself fine- both physically and magically. Honestly, Jim was stronger than he was despite the size difference.

"Why did you hurt him?" Jim snarled, his eyes furious and dark.

"He has some control over you." Sebastian choked out painfully, flinching at the hand tightening. "Spell- love potion." His vision was starting to dim and he was honestly worried that Jim was going to strangle him then and there.

"Are you questioning my authority, Sebby?" Jim's voice sounded playful, with a undertone of coldness. This was a voice he usually only reserved for Sherlock or torture sessions. Sebastian became acutely aware or the bruises he would have on his throat tomorrow.

"No, sir." Sebastian choked out.

"Never do this again or I will not hesitate to kill you, useful or no."

With that, Jim let go of him and unbound his hands. Sebastian leaned against the wall, wincing as air scratched into his lungs.

"Don't think your punishment is over, Seb. You and I are going to have a nice walk in the Forbidden Forest." Jim said quietly before turning around to Professor Holmes who had managed to get Sherlock in the safest position possible.

His face became expressionless and he stood up. Without wasting another second, the professor sent a Patronus to the nurse and Headmistress before turning to face Sebastian.

"What happened here?" His cold eyes were trained on Sebastian and he felt a cold sweat come over him. He had already been under the scrutiny of one genius.

"John Watson tried to attack me, and when I tried to talk to him, he tried to curse me and I was given no other choice, sir."

Sebastian knew that Professor Holmes didn't believe a word of it, but something in his eyes clicked and he turned to John who was still lying on the ground. He took him out of the Body Bind and Watson sat up intermediately, turning to the professor.

"He's lying, Professor. I didn't do any of that!"

"This is the second time in the last twenty four hours that you have put a student in danger, Mr. Watson. Why don't you say the truth?" Professor Holmes said coldly.

Watson looked stricken and he hastily stood up but before he could say anything Headmistress Granger, Nurse White, and Professor Malfoy rushed into the room.

"Dear Merlin, what happened here?" Nurse White exclaimed as she rushed over to Sherlock who had fallen unconscious by this point. She levitated him and carried him out the door, a trail of blood droplets following her.

"John Watson attacked Sebastian Moran who used Sectumsempra in self defence but Sherlock jumped in the way." Mycroft delivered coldly.

"Headmistress, I did nothing!" John looked like he was at the point of tears. He was trembling, pale in the face.

"Of course you would say that," Professor Malfoy took a step towards the boy.

"Why did he attack you?" Headmistress Granger gave a short glare to Malfoy before turning her attention to John.

"I don't know! One second we were practising the Expelleriamus and the next he tried to curse me." John ran a hand through his hair.

"Sebastian is one of the best students Hogwarts has." Professor Malfoy scowled. "You should stop lying, Watson. It just reflects on your terrible upbringing as a Mudblood."

Everyone turned to the professor in shock, and Headmistress Granger looked furious.

"Malfoy, I suggest you take that statement back, or so help me-"

"What are you going to do, Granger?" Malfoy sneered, flipping out his wand. "It's true. This school is infested with your precious little Mudbloods who are only contaminating the Wizarding population with their attempts at joining this world."

Jim quickly grabbed Sebastian's arm and yanked him behind the desks, crouching.

Headmistress Granger looked somewhere between shocked and outraged, and she flipped out her wand and sent a silent Incarcerous. The professor dodged it and sent a Bombarda. A flurry of spells and curses weaved between them, narrowly missing her. As the fight ensued, Professor Holmes ushered out all the students.

Sebastian had his attention solely on the Headmistress and Professor Malfoy, not even noticing how Professor Holmes locked the door behind him and was now edging towards the intense fight.

"This is going to be interesting to see." Jim smirked. Granger's back was to Professor Holmes and he pointed his wand at her.

"Headmistress, watch out!"

In slow motion, John ,who had seemed to have escaped the mass exodus, launched himself at the professor. They landed hard on the ground, where John slapped the other's wand away and cast a Body Bind on him.

"It seems you have a little warrior on your side." Malfoy smirked, a trail of blood coming from his mouth. Granger glared at him, clutching her arm that had been broken. Her face was a web of cuts, a nasty looking one right above her lip.

"I thought this silly prejudice over, Malfoy."

"Expulso!"

Her wand flew from her weak grasp and she fell unconscious. John scrambled over to the Headmistress, but he was stopped by a wand at his neck. The Gryffindor glared up at the blond-haired man who held his trademark sneer on his face.

"It's too bad you're a Mudblood, Watson. You would make the perfect soldier."

Out of the corner of his eye, he saw Jim stand up and Sebastian moved to stop him but the Slytherin strode over to the professor.

"Professor Malfoy, I would advice against killing him."

John looked over in confusion.

"And why is that?"

"John is bound to me by Fidelius."

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><p><strong>So I've been getting some hardcore awesome reviews and I want to thank you all who have reviewed. You really make my day and it inspires me to write.<strong>

**Also, if you have any suggestions or just want to see something like idk, something cute or dark, please do not hesitate to ask for it. I will work in ANYTHING. (Sometimes not immediately, but it will be woven in eventually) Or, if you just want to give a suggestion, please do. I'm a novice writer, trying to write long ass fanfics. **

**Thank you and leave a comment below. Once again I do not have a wifi and will be posting at random intervals of time. So follow/ subscribe. I love you all!**


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